| The artificial retaining walls or surrounding rocks in mine roadways,tunnels and other places have the migration and exhalation of radon caused by radium decay,and the radon exhaled from the surface will cause radiation harm to the living or working people in these places.Therefore,the radon pollution caused by the artificial surrounding wall or the surrounding rock in the above-mentioned place is an urgent problem to be solved.According to the characteristics of uranium mine tunnels,it is abstracted into a circular tubular porous emanation medium.A mathematical model of the diffusion migration of radon from the circular tubular porous emanation medium,a mathematical model of the seepage-diffusion migration of radon from the circular tubular porous emanation medium,a mathematical model for seepage-diffusion migration of radon from a multi-layer porous emanation medium combined with a thin-walled circular tubular porous emanation medium and a thick-walled circular tubular porous emanation medium are established.Through theoretical analysis,experimental research and numerical simulation,the rule of radon transport and exhalation in a circular tubular porous emanation medium was studied,and the following conclusions were obtained:(1)Based on a mathematical model of the diffusion migration of radon from the circular tubular porous emanation medium,a method to determine these two parameters in compact porous emanation media was proposed,and an experimental measuring device was designed and manufactured.The experimental device was used to simultaneously measure the radon exhalation rate from the inner and outer surfaces of a quarter-circular tubular concrete block filled with fine-grained uranium tailing sand.The measurements were used to calculate the radon diffusion coefficient and the free radon production rate.The result obtained by using this method shows that accuracy was within the accepted range of experimental error(2)Based on a mathematical model of the seepage-diffusion migration of radon from the circular tubular porous emanation medium,the radon exhalation rate of the inner and outer surfaces of the 1/4 circular tubular block piece under different pressure gradients was determined by a self-made experimental device.This results show that the experimental results for the radon exhalation rate and the total amount of radon exhalation are in good agreement with the theoretical calculation values,the radon emanation rate at the low-pressure side increases with the increase of seepage velocity(pressure difference),while the radon emanation rate at the high-pressure side is on the contrary.The total amount of radon exhalation per unit time increased as the seepage velocity increased and tended toward a maximum value.This results also show the experimental device and measuring method for the exhalation of radon from a circular tubular porous media are feasible.(3)Based on a mathematical model for seepage-diffusion migration of radon from a multi-layer porous emanation medium,the effects of the thickness of the covering,the radon diffusion coefficient of the covering and the seepage on radon exhalation were studied by numerical simulation.According to the research results,the following conclusions are drawn:When there is no seepage,radon exhalation rate in covering layer decreases with the increase of covering thickness and tends to 0.Radon exhalation rate in covering layer increases with the increase of radon diffusion coefficient.In the case of seepage,the more thick covering is,the smaller difference of radon exhalation between seepage and non-seepage is.When v>0,radon exhalation rate in covering layer increases with the increase of seepage velocity.When v<0,radon exhalation rate in covering layer decreases with the increase of seepage velocity. |
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